Seal Stock Laminate

ABSTRACT

A method for producing a primary laminate including a tabstock by feeding a seal laminate comprising bottom food contact layers including a foil layer and a top polyester layer to a laminating station wherein either the foil layer of the underside of the polyester layer has been printed; simultaneously feeding a tabstock, which is narrower than the seal laminate, to the laminating station such that the bottom of the tabstock and the top polyester layer of the seal laminate come into contact to form a primary substrate, simultaneously feeding a plastic film stock; and continuously extruding a polymeric adhesive between the top face of the primary substrate and bottom surface of the plastic film stock.

The present invention relates to a method of making a laminate which isused in container closure systems. The laminate produced is a primarylaminate stock including a tabstock which can then be attached to asecondary seal and used for re-closing a container using a screw cap.

It is commonplace in the packaging of a wide variety of materialsranging from pharmaceutical products to instant coffee that a closure isprovided in the form of a seal connected to the neck of a container anda screw cap covering and protecting the seal which provides are-closable cap after the seal has been removed to gain access to thecontainer. Often the closure is such that the underside of the seal hasa heat sensitive adhesive coating or a meltable plastics layer coveredby a metal foil. The metal foil can provide the substrate of the seal ormay include a separate substrate formed from plastics material or paper.The seal is then placed against the neck of a container and sandwichedagainst it by the applied screw cap. An induction heating step thenheats the metal foil and in turn activates the heat sensitive adhesivelayer or melts the plastic layer so that on cooling, the seal bonds tothe neck of the container. A difficultly often encountered by eventualusers is removal of such seals from the container. Attempts have thusbeen made to include a tab extending sideways from the neck of thecontainer so that the consumer can grip this to facilitate removal ofthe seal.

Single component systems have been developed wherein the primary sealand secondary liner are produced as a laminate disk which is attachedwithin the cap. The commercially available Quadraseal™ system is anexample of a single component system. The bottom layer of the sealportion is formed of glassine which is attached to a foil layer by meansof a wax based adhesvive. Upon removal of a cap into which the system isfitted, the seal portion remains adhered to the neck of the container.It can be removed by puncturing the seal and tearing it off in pieces.Due to failure of the glassine fibres, there will be traces of fibresremaining adhered around the circumference of the neck.

A further example is DE9108868 in which the primary seal and secondaryliner are adhered by means of wax. On heating of the metal foil in theprimary seal portion the wax melts and is absorbed into the secondaryliner whereby the primary seal and secondary liner substantiallyseparate from each other. On opening the primary seal remains adhered tothe container and the secondary liner remains in the cap. This systemincludes a tab which is formed by only adhering the top layer of primaryseal to the remainder of the seal across part of the diameter of theseal. One problem with this system is that there are residues of waxmaterial left on the surface of the liner such that when the containeris resealed, some of the contents of the container may stick to theliner surface or may be released into the container itself. In thepackaging of food and pharmaceuticals, such a wax residue isundesirable. Attempts have therefore focussed on the use of a plasticsbased means for adhering the primary seal to the secondary liner as aso-called release layer to avoid the use of wax. It is also verydifficult to ensure that during attachment of the seal to the containerto be sealed, the heat produced does not cause the delaminated portionwhich forms the tab to adhere to the remainder of the primary sealportion.

A further example of a system including a tab structure is the “Top Tab”structure disclosed is U.S. Pat. No. 4,961,986. This structure includesa multilayer primary seal, one layer of which is partly de-laminated toprovide a lifting tab lying wholly within the circumference of thecontainer neck in use. This system is essentially a system comprising aprimary seal and secondary liner whereby the secondary liner has beenadhered to a cap. The primary seal is then pushed into the cap and heldin place by engagement with the screw thread within the cap. In thissystem, the tabs are adhered to the primary seal by applying an adhesivelayer in strips and then adhering the top layer with the result that itis only stuck in particular portions where the adhesive was present.Such a method is time consuming as it involves the graduallayer-by-layer construction of the primary seal including the tab andinvolves the use of a specifically formed roller to apply the adhesivein strips.

A further tab system is the successful “Lift “n” Peel”™ commercialsystem. This can be comprised of a primary seal and a secondary liner orjust a primary seal and is usually just a primary seal. The primary sealincludes a thick layer of foam such that the seal can be a product inits own right without requiring a secondary liner to give it stability.The thickness of the foam allows for discrepancies in the container orcap size. However, the foam is expensive and the resulting primary sealis difficult to manipulate. A further disadvantage associated withincluding foam is that it is not a printable substrate. Nowadays,consumers rely heavily on the labelling of goods and it is desirable tobe able to provide a seal that is printed to indicate the manufacturer.It is usual that the printing is done on the foil layer included withinthe heat induction layers. This will only be seen where the layers ontop of the metal foil are transparent. The “Lift “n” Peel” system doesnot present this opportunity due to the opaque nature of the foam. Thetop layer of the Lift “n” Peel system is a particular polyethyleneterephthalate/ethylene vinyl acetate (PET/EVA) structure. The presenceof EVA is necessary to ensure adhesion to both the PET tab and the foam.If the EVA were to be printed then this would interfere with theadhesion properties it exhibits. Hence reverse i.e. printing theunderside of the top layer of the “Lift “n” Peel” system is not a viableoption. The PET/EVA structure used is an expensive material andadditionally requires the use of heated rollers to melt the EVAcomponent of the structure to achieve adhesion. The lower the amount ofEVA used, the greater the size of the heated roll required. Thus to usea material of low cost which contains minimal EVA, the size of the rollrequired becomes prohibitively large and expensive.

In WO 97/02997, a method for including a tab in a primary seal laminateis disclosed. In this case three feeds are passed to a chill roll incontact with a nip roll. The first feed which will form the top layer ofthe primary seal laminate, is EVOH coated with polypropylene. The secondfeed is a deadening member and the third feed is extruded tabstock e.g.polypropylene. All three feeds come into contact at the point where thechill roll and nip roll are in contact. The chill roll quenches theextruded tabstock maximising its amorphous properties and causeslamination of all three layers.

It is therefore clear that there is a need for a simple and costeffective method for including a tabstock in a primary seal laminate.Such a method should avoid the problems associated with the prior artsuch as having to carry out step-by-step lamination, producing anineffective tab or the necessity to use expensive equipment andmaterials. It would be advantageous in the current market to produce aprimary laminate including a tab which is printed or coloured.

The apparatus required must have separate unwind stations for thelaminate feeds that are arranged to enable simultaneous unwinding. Thelaminate feeds are fed to a lamination station comprising two rollers incontact with each other. At this point the feeds are adhered to eachother to produce the laminate including a tabstock which is subsequentlywound onto a final roll and can then be passed through the sameapparatus and adhered to a secondary laminate. The adhesive is appliedvertically downwards onto the point where the feed rollers are incontact. The speed of the feed rollers should be faster than the rate ofapplication of adhesive. The adhesive can be applied directly from thedie head of an extruder.

The present invention provides a method for producing a primary laminateincluding a tabstock the method comprising the steps of:

a) feeding a seal laminate comprising bottom food contact layersincluding a foil layer and a top polyester layer to a laminatingstation;

b) feeding a tabstock, which is narrower than the seal laminate, to thelaminating station such that the bottom of the tabstock and the toppolyester layer of the seal laminate come into contact to form a primarysubstrate, the top face of which is partly comprised of the top face ofthe tabstock and partly comprised of the top polyester layer of the seallaminate, prior to reaching the laminating station;

c) feeding a plastic film stock which has a top and bottom surface tothe laminating station; and

d) continuously extruding a polymeric adhesive between the top face ofthe primary substrate and the bottom surface of the plastic film stocksuch that the two are adhered together with a bond strength greater than15 N/cm when the tabstock is pulled at 90° to the machine direction and180° to the primary substrate, to form a primary laminate including atabstock.

In one embodiment of the present invention, the bottom food contactlayers of the seal laminate are induction heat sealable and comprise alayer of aluminium foil coated on its lowermost face which willultimately be in contact with the neck of a container with a layer ofhot melt adhesive. A layer of polyethylene terephthalate may beinterposed between the hot melt adhesive and aluminium foil layer toisolate the foil from the contents of any container to which it isattached and so prevent corrosion of the foil layer. This polyethyleneterephthalate layer generally has a thickness in the range from 10 to 14μm. It is attached to the foil layer using either a solvent orsolvent-less adhesive lamination. Where it is included, the polyethyleneterephthalate has already been attached to the foil layer by thesupplier. Preferably the thickness of the foil layer is in the rangefrom 12-30 μm.

In a further embodiment of the present invention the bottom food contactlayers of the seal laminate are conduction heat sealable.

In a yet further embodiment of the present invention, the bottom foodcontact layer of the seal laminate comprise a layer comprising a layerof metal foil coated on its lowermost face which will ultimately be incontact with the neck of a container with glassine. Glassine is a paperbased material which is formed from pulp which has been beaten to theextent that its constituent fibres are all very short resulting in abrittle material which is almost transparent. Glassine is commerciallyavailable from, for example, Ahlstrom in France. The glassine is adheredto the lowermost face of the metal foil by a layer of adhesive. Whileconventionally in such a system, a wax based adhesive would be used toadhere the glassine to the foil, it is preferable in the invention touse a polyethylene-based or a water-based adhesive in order to ensure asufficiently strong bond is formed.

The bottom glassine layer of the primary laminate may be adhered to theneck of a container using a conventional adhesive such as, for example,PVA. In this embodiment, the thickness of the foil layer may be as lowas 9 μm. In use, where the primary laminate is removed from a containerneck, failure will occur in the glassine layer such that paper fibresremain adhered to the neck of the container but the primary laminate isstill removed as a single piece. The advantage of the paper fibresremaining adhered to the neck is that it provides a tamper evidentsystem.

The foil layer may optionally be printed such that the identity of themanufacturer of the ultimate contents of any container to which theprimary laminate is adhered is evident. Consumers view this as aguarantee of safety, quality and of the origin of the contents. Wherethe foil layer is printed, this will have been done by the supplier ofthe foil layer.

The top layer of the seal laminate is a layer of polyester. Such a layeris included in order to impart strength into the primary seal laminatesuch that it can not simply be ripped or broken easily manually.Additionally, including this layer means that the print is not in directcontact with the extruded polymeric adhesive and thus elimination ofpotentially problematic interactions. Preferably the thickness of thetop polyester layer is at least 12 μm. A preferred thickness is in therange from 12 to 25 μm In a preferred embodiment of the presentinvention, the polyester is polyethylene terephthalate. Where the toppolyester layer of the seal laminate is polyethylene terephthalate, itis preferable that prior to being contact with the polymeric adhesive,it has been corona treated.

As is clear, it is preferable that one of the components of the primaryseal laminate is printed. This can be achieved by including a foil layerwith a preprinted upper face in the heat sealable layers. Alternatively,the underneath of the polyester layer which will not be in contact withthe polymeric adhesive can be printed. In both cases it is required thatthe polyester layer is transparent such that the printing on either themetal foil or underneath of the polyester layer is immediately visibleto the end user. The printing is carried out prior to the inclusion ofthe tabstock.

The primary seal laminate formed includes a free tab as is included inthe “Top Tab”™ and “Lift “n” Peel”™ structures described in U.S. Pat.No. 4,961,986. In the primary seal laminate produced, while the relativedimensions of the tab are not limited, it may be preferable that, forexample the tab lies wholly within the circumference of the containerneck and typically the tab occupies about 50% of the seal area, wherethe primary laminate has a diameter of less than 36 mm. The tab isprovided by adhering a tab stock to the top polyester layer of the heatsealable laminate.

The tabstock which is fed to the laminating station as detailed in step(b) is narrower in width than the heat sealable laminate. Preferably thetabstock is formed of a polyester, more preferably polyethyleneterephthalate. In one embodiment of the present invention, the bottomsurface of the tabstock which is ultimately in contact with the toppolyester layer of the heat sealable laminate may be coated with arelease material, for example, silicone. This is done in order tofurther ensure that when the finished primary seal laminate is adheredto a container by induction heat sealing, the tabstock does not stick tothe top polyester layer. The tabstock may further include a coloured orprinted layer formed of polyester and attached to the other polyesterlayer by an adhesive tie layer.

In step (b), in one embodiment of the present invention, rather thanfeeding a single tabstock, the feed may comprise a plurality of narrowtabstocks arranged at regularly spaced apart intervals. In this way, awide sheet of primary laminate including a tabstock may be formed whichcan then be cut as required thus improving the efficiency of the system.

As detailed in step (c), the third feed which is fed to the laminatingstation is a plastic film stock. Preferably the plastic film is selectedfrom the group consisting of polyethylene terepthalate, polyamide,polypropylene or a composite. Most preferably the plastic film ispolyethylene terephthalate. The width of this stock is the same as thewidth of the heat sealable laminate. This plastic film layer must betransparent in order that the printing of the lower layers is visible tothe end user. Preferably the thickness of the plastic film layer is atleast 12 μm. More preferably the thickness of the plastic film layer isin the range from 12-36 μm. In a preferred embodiment of the presentinvention, where plastic film is PET stock, preferably it is bothcoextruded and corona treated. This is done in order to ensure that thebond formed to the polymeric adhesive in step (d) is sufficientlystrong. The PET stock can be obtained in a coextruded state. Examples ofsuitable materials include Lumirror 10.47 which is a film that iscoextruded on one side and are commercially available from Toray.

Prior to reaching the laminating station, the bottom face of thetabstock and the top PET layer of the seal laminate are brought intocontact. At this stage, there is no adhesion between the two feeds. Thetwo feeds are fed in contact with one another to the laminating station.In order to achieve this, the two feeds must approach the laminatingstation from the same side. The combination of the seal laminate andtabstock in contact with each other is referred to as a primarysubstrate as they are passed to the laminating station together. As thetabstock is necessarily narrower in width than the seal laminate, thetop face of the primary substrate presented to the laminating station isformed partly of the top face of the tabstock and partly of the toppolyester layer of the seal laminate.

In the laminating station, the primary substrate is brought into contactwith the plastic film stock which is fed simultaneously to thelaminating station but from the opposite side. At the point where thetop face of the primary substrate is in contact with the bottom surfaceof the plastic film stock, a polymeric adhesive is continuously extrudedbetween the two surfaces. The result is that the plastic film stock isadhered over the entire surface area of the top face of the primarysubstrate. This means that over part of the width, the plastic stockwill be adhered to the top plastic film layer of the seal laminate andover the remaining width the plastic film stock will be adhered to thetop face of the tabstock. The result is then that a tab portion isformed which lies wholly within the circumference of the primarylaminate formed.

The bond formed between the top plastic film layer of the seal laminateand the plastic film stock must have a strength in the greater than 15N/cm when the tab is pulled at 90° to the machine direction and 180° tothe primary substrate. This is in order to ensure that when using thetab to remove the seal from a container, the tab remains adhered to theprimary laminate upon application of a pulling force to the tab.

Preferably the polymeric adhesive which is continuously extruded isselected from polyethylene, polyethylene vinyl acetate, maleicanhydride/acrylate ester/polyethylene copolymer and ethylene methylacrylate. Most preferably the polymeric adhesive has a melt flow indexin the range from 1 to 17 dg/min. Preferably the coat weight of theadhesive layer is at least 30 gm⁻².

In a preferred embodiment the coat weight of the adhesive layer is inthe range from 20 to 40 gm⁻². In a preferred embodiment, the polymericadhesive is an ethylene methyl acrylate co-polymer.

In order that any printing can be seen, preferably the polymericadhesive and the plastic film stock are transparent.

The primary laminate including a tabstock as made according to thepresent invention may then be attached to a secondary seal stock so asto form a one component seal and liner system. This can be done usingthe same apparatus as used to form the primary laminate including atabstock. More specifically, the method involves the steps of:

feeding the primary laminate including a tabstock to a laminatingstation;

simultaneously feeding a secondary seal stock which has an overallstiffness in the range from 200-1200 gcm and has an upper face forcontact with a container closure and a lower face for sealing against acontainer to the laminating station; and

extruding a polymeric adhesive with a melt flow index in the range from5-17 dg/min through a die head between the top plastic film face of theprimary laminate including a tabstock and lower face of the secondaryseal stock to adhere the two to form a seal stock laminate.

The secondary seal stock of the present invention has a stiffness in therange from 200-1200 gcm. This stiffness is measured according to theTeledyne Taber V-S Stiffness Tester (Model 150-B). The method employedinvolves cutting the test samples to size of 3.8 cm by 7 cm (1.5×2.75inches) one with the grain of the board and one at right angles to thegrain. The test is carried out at room temperature. The top of thesample is then clamped so that it is central, parallel to the testerface and the bottom of the sample is resting on the plate below therollers of the machine. The right hand roller is brought up to justtouch the bottom of the sample without deflecting it. The left handroller is brought into light contact with the sample and then backed offby a quarter of a turn. Care is taken to ensure that the scale, drivingdisc and pendulum are all aligned at zero. The sample is deflected inone direction by pushing the operating switch until the pendulum is at15°. The value on the fixed scale is recorded. The direction of thependulum is then reversed and the sample is deflected in the oppositedirection by 15° and the value is recorded from the fixed scale. Theaverage of the two values is taken and the appropriate weightmultiplication factor is used to determine the stiffness in Taber units(gcm)

In some embodiments, where a secondary seal stock is included, it may beformed of pulpboard or folding box board. Alternatively, the secondaryseal stock may be a synthetic laminate. Where the secondary seal stockis a synthetic laminate it is preferable that it comprises a foam with afacing layer on each face thereof. The thickness of the foam layer ispreferably in the range from 0.85-1.65 mm and suitable materials includepolyethylene and polypropylene foam. The thickness of the facing layersis preferably in the range from 20-70 μm.

The facing layers may comprise a single layer, for example apolyethylene terephthalate, polyethylene, polypropylene or polyamidefilm, or alternatively may comprise multilayers. The nature of thefacing layer depends on the nature of the foam layer and the polymericadhesive. Where a facing layer which is equally compatible with both thefoam layer and polymeric adhesive cannot be found, it is necessary forthe facing layers to be multilayer to achieve a graded layer which willadhere tightly to the adhesive and subsequently the foam. The gradedlayers will tend to be able to heat seal to itself. Where the facinglayers are multilayer, it is preferred that the facing layers comprise ahomopolymer core with a copolymer layer on each face thereof. Thehomopolymer core is chosen to ensure that the synthetic laminate has theappropriate stiffness.

In one embodiment of the present invention where a secondary seal stockis adhered to the primary laminate, the foam layer is polyethylene foamand the facing layers are comprised of three layers, specifically ahomopolymer core with copolymer layers on each face thereof wherein thehomopolymer core comprises polypropylene and the copolymer is apolyethylene/polypropylene copolymer. Inclusion of the polypropylenehomopolymer layer ensures that the synthetic laminate has theappropriate stiffness. Such a secondary seal stock can be obtainedcommercially or can be produced by lamination as required.

In this embodiment of the present invention where the foam layer ispolyethylene foam and the facing layers are comprised of a polypropylenecore with polypropylene/polyethylene copolymer layers on each facethereof preferably the polymeric adhesive is provided by coextrudingpolypropylene and polyethylene through the die head such that thepolypropylene is in contact with the lower face of the secondary sealstock and the polyethylene is in contact with the top plastic film faceof the primary laminate.

In order to adhere the primary seal laminate to the secondary sealstock, a polymeric adhesive is extruded between the top plastic filmface of the primary seal laminate and the lower face of the secondaryseal stock. The polymeric adhesive must have a melt flow index in therange of 5-25 dg/min. The method used to determine the melt flow indexis International Standard ISO 113/ASTM D 1238.

The strengths of the different bonds formed in the seal stock laminateare important. In use, the bond formed between the food contact layer ofthe laminate and the neck of the container which it is used to seal,should be sufficiently strong that the primary laminate remains adheredto the neck of the container when the lid is removed and a complete sealis maintained. It should, however, be weaker than the strength of thebond at the point of contact between the top layer of the seal laminateand the tabstock.

Where a secondary seal stock is adhered to the primary laminate, apolymeric adhesive with a melt flow index in the quoted range isrequired in order to ensure that a true weld is formed between theadhesive and the lower face of the secondary seal stock while the bondformed between the adhesive and the top plastic film layer of theprimary laminate is not a true weld. In order to achieve this, the twosurfaces in contact with the adhesive must be different. The adhesivemust bond more strongly to the lower face of the secondary seal stockthan the top plastic film layer of the primary seal laminate. The topplastic film layer of the primary laminate is therefore required to havea higher surface energy than the lower face of the second seal stock.The term “true weld” refers to the fact that a bond is formed betweenthe adhesive and the lower face of the secondary seal stock such that ifan attempt is made to separate the adhesive and lower face of thesecondary seal, the adhesive material and lower face material tend tofail in preference to the bond. Preferably the bond formed between thepolymeric adhesive and the top plastic layer of the primary seal stockhas a peel strength in the range 50-130 g as measured on a 25 mm widestrip at 1500 mm/min. This means that in use, upon application of atorque to the cap of a container to which the seal stock laminate isattached the bond between the top plastic film stock layer of theprimary laminate and the polymeric adhesive will break such that theprimary laminate remains adhered to the container while the secondaryseal stock would remain in the cap.

Where the seal stock laminate is attached to a container fitted with ascrew cap, on turning the screw cap, the end user will break the bondand hear a “cracking noise”. Where such a noise is heard it providesevidence that the container has not been tampered with. Suitablepolymeric adhesives include low density polyethylene or coextrudedpolyethylene and polypropylene. Preferably the polymeric adhesive ispolyethylene. The seal stock laminate is intended for use on closureswith neck sizes of up to at least 100 mm in diameter.

The polymeric adhesive is extruded through a die head. The length of thedie head is preferably in the range from 500 to 2000 mm. The gap of thedie head is preferably in the range 450 to 800 μm more preferably, thegap is in the range from 500 to 700 μm. The speed of the feed rollers isin the range from 50 to 120 m/min. A typical speed of the feed rollersis, for example, 100 m/min.

The seal stock laminate of the present invention is generally formed inwide strips. Therefore in order to form the tabs, it is necessary to cutthe wide strips of seal stock laminate into narrower strips. Thesenarrower strips can then be cut to form a vessel closing assembly readyto be applied to a container. The cutting of the wide strips intonarrower strips needs to be done with precision in order to ensure thatthe cuts are made at the correct positions to produce the tabs. Thevessel closing assembly supplied ready to be used in the form of tapescan then be punched from the narrower strips and fixed inside the top ofa screw cap in a procedure and/or location separate to the method ofmaking the seal stock laminate. Unlike a conventional screw cap thescrew cap suitable for use in the present invention must include aretention feature. Preferably the retention feature is quadrant shapedon top and flat underneath to minimise damage on insertion of the vesselclosing assembly. The retention feature may include a multi-turnscrew-thread or a mult-start part turn thread. The container may be madeof glass or plastic material such as polyethylene, polyester, polyvinylchloride, polypropylene or acrylonitrite-butadiene-styrene polymer.

A screw cap equipped with a vessel closing assembly in accordance withthe present invention may be screwed on to the open neck of a containerthus sandwiching the vessel closing assembly between the open neck ofthe container and the top of the cap. The primary laminate is thenadhered to the open neck of the container by induction heating.

An embodiment of the present invention will now be described withreference to the following figures, in which:

FIG. 1 is a cross section through an example of a primary laminateincluding a tabstock as formed according to the method of the presentinvention with a vertical dimension greatly exaggerated.

FIG. 2 is a schematic diagram of the laminating apparatus used in themethod of the present invention.

FIG. 3 is a cross section through an example of the seal stock laminatewith a vertical dimension greatly exaggerated.

FIG. 4 is a cross-section through a screw cap showing the vessel closingassembly in place.

FIG. 5 is a perspective view showing the seal in place on the neck of acontainer.

FIG. 6 is a cross section through a second embodiment of a primarylaminate including a tabstock as formed according to the method of thepresent invention with a vertical dimension greatly exaggerated.

EXAMPLE 1

A seal laminate (1) was obtained commercially from Gerosa, Spain. Theseal laminate comprised heat sealable layers (2,3) for adhesion to acontainer to be sealed and a foil layer (4). The top layer of the seallaminate (5) is PET which has been printed on the reverse side. As analternative to purchasing this part of the structure (2, 3, 4) as inthis example, it may be laminated to the foil layer in a separate stepto form the heat sealable laminate. This seal laminate is rolled onto afirst feed roll (9) in the laminating apparatus.

The second feed roll (10) in the laminating apparatus is the source ofthe tabstock (6). The tabstock used is formed of PET which has athickness in the range from 12-25 μm. The width of the (6) is in therange from 20-60 mm.

A third feed roll (11) is loaded with a PET stock (8) which can beobtained commercially from Toray, Europe. The thickness of the PET stock(8) is in the range from 12-36 μm. The PET stock (8) used is aco-extruded PET heat seal layer in order to ensure optimal adhesion.

The seal laminate (1), tabstock (6) and PET stock (8) are simultaneouslyfed to the laminating station (12) where an extruder (13) is positionedvertically above the point of contact between the feeds. Prior toreaching the laminating station (12), the seal laminate (1) and tabstock(6) are brought into contact to form a primary substrate (1 a).

Ethylene methyl acrylate copolymer (7) is then extruded continuously asa curtain from the extruder (13) between the top face of the primarylaminate (la) and the bottom face of the PET stock (8). The extrusionconditions were such that a temperature of 100° C. to 200° C. wasattained at the nip. The rollers (14) and (21) are moving at a speed of70 m/min relative to the speed of application of the adhesive. thebottom face of the PET. Stock (8) and the resulting primary laminateincluding a tabstock is passed via a chill roller (14) to be rolled onto a final product roll (15). This process is illustrated schematicallyin FIG. 2.

The peel strength of a primary laminate formed using a PET stock (8)thickness of 36 μm and a tabstock thickness of 12 μm wherein the coatweight of the extruded ethylene methyl acrylate copolymer (7) was 40gm⁻³.

The coat weight was determined as follows: a 0.5 m to 1 m length ofpaper backed polyester which has a width of 1m was passed to thelaminating station in place of the primary laminate. A curtain of EVAwas then extruded continuously between the top polyester face of thepaper backed polyester and the bottom face of the PET stock (8). 10×10cm samples were then cut across the width of the web and their weight ing was recorded. The weight of the paper backed polyester and PET stock(8) were subtracted from this figure and the result was multiplied by100 to give a coat weight in gm⁻².

As detailed previously, the top face of the primary substrate and thebottom surface of the plastic film stock must be adhered together with abond strength greater than 15 N/cm. In a separate experiment the bondstrength was determined by using the method detailed as follows. Theapparatus used was a Tensile Tester attached to a desktop PC, two jaws,a 80×12.5 mm measuring template and a sharp knife. A sample withdimensions of 12.5 mm long and 10 mm wide perpendicular to the machinedirection was cut across a section of the primary laminate. Steps aretaken to ensure that a section of the PET stock (8) and the primarylaminate including a tabstock is separated. The height of the jaws isadjusted such that the tab is inserted into one and the base into theother. The sample is positioned so as to be pointing towards themachine. The tab and base are then pulled apart and the force requiredto do so is recorded from the apparatus.

EXAMPLE 2

The primary laminate including a tabstock (1 b) as formed in Example 1was then adhered to a secondary seal stock to form a one component sealand liner system. The secondary seal stock (17) was manufactured on siteat Unipac and comprises a foam layer with a thickness of 1.25 mm whichis polyethylene foam (18) faced with layers on either side ofpolypropylene film (19). The stiffness was 320 gcm.

The same apparatus as was used to form the primary laminate including atabstock (1 b) detailed in Example 1 was used. The primary laminateincluding a tabstock was loaded onto feed roll (11) and the secondaryseal stock (17) was loaded onto the third feed roll (9). In this case,the second feed roll (10) was redundant and thus not used. The primarylaminate including a tabstock and secondary seal stock (17) were fedsimultaneously to the laminating station (12). A curtain of low densitypolyethylene (16) with a melt flow index of 7.5 dg/min and polypropylene(16 a) with an MFI of 11 dg/min was extruded continuously from theextruder between the top polyester face (8) of the primary laminateincluding a tabstock and the lower face of the secondary seal stock (19a) adhering the two to form a seal stock laminate (20) wherein thepolypropylene (16 a) adheres to the lower face of the secondary sealstock (19 a) and the polyethylene (16) adheres to the top polyester face(8).

The seal stock laminate was then cut into narrow strips. From thesestrips, circular discs were punched to form discs of the seal stocklaminate. The seal stock laminate (20) is fixed inside the top of ascrew cap (22) by means of a retention feature (23). A screw capequipped with the seal stock laminate in accordance with the presentinvention is then screwed onto the open neck of the cap. The cap (22)and bottle (24) are then subjected to an induction heating step in whichthe foil is heated around its periphery by the generation of eddycurrents within it, which, in turn, melts the heat sealable layer (2) tobond the primary laminate including a tabstock to the open neck of thebottle.

EXAMPLE 3

A seal laminate (29) comprising bottom food contact layers (25, 26) foradhesion to a container to be sealed and a foil layer (27) which hasbeen printed are purchased from Gerosa, Spain. The lowermost layer (25)of the seal laminate consists of glassine paper with a coat weight of atleast 30 gm⁻². Layer (26) is a layer of water-based adhesive with a coatweight of at least 3 gm⁻² (dry weight). The layer of aluminium foil (27)has a thickness of 8 μm. The top layer of the seal laminate (28) is PET.This is purchased as a part of the structure (25, 26, 27) or laminatedto the foil layer in a separate step to form the seal laminate.

The primary laminate was formed using this seal laminate (29) in placeof the seal laminate (1) having heat induction sealable layers ofexample 1 to produce a primary laminate. The resulting primary laminateis illustrated in FIG. 6.

1.-42. (canceled)
 43. A primary laminate configured to form a tabbedcontainer sealing member having a tab defined wholly within a perimeterthereof, the primary laminate comprising: a seal laminate including atleast a bottom layer for securing to a rim surrounding a containeropening, a foil layer, and a top polyester film layer; a tab stock filmlayer with a top and bottom face wherein the bottom face of the tabstock film layer is above the top polyester film layer of the seallaminate to form a primary substrate; an upper surface of the primarysubstrate having a first and a second portion wherein the first portionis formed by the top polyester film layer and the second portion isformed by the top face of the tab stock film layer; a layer of plasticfilm adhered to both the top face of the tab stock film layer and thetop polyester film layer by an extruded polymeric adhesive, the layer ofplastic film selected from polyethylene terephthalate, polyamide,polypropylene or a composite thereof, and the extruded polymericadhesive selected from polyethylene, polyethylene vinyl acetate, maleicanhydride/acrylate ester/polyethylene copolymer, and ethylene methylacrylate; and a bond between the layer of plastic film and the toppolyester film layer formed by the layer of extruded polymeric adhesiveof at least about 15 N/cm; wherein the upper surface of the primarysubstrate is free of printing that interferes with the bond formedbetween the layer of plastic film and the top polyester film layer. 44.The primary laminate of claim 43, wherein one of the foil layer or anunderside of the top polyester film layer facing the foil layer isprinted so that the printing is not in direct contact with the extrudedpolymeric adhesive, and the layer of plastic film, the top polyesterfilm layer, and the extruded polymeric adhesive are transparent so thatthe printing is visible through the top of the primary laminate.
 45. Theprimary laminate of claim 43, wherein the extruded polymeric adhesive isethylene methyl acrylate, the layer of plastic film is polyethyleneterephthalate, and the top polyester film layer is polyethyleneterephthalate.
 46. The primary laminate according to claim 43, furthercomprising a secondary seal stock having an overall stiffness in therange from 200-1200 gcm and wherein the layer of plastic film of theprimary laminate is bonded to the secondary seal stock by a secondextruded polymeric adhesive having a melt flow index of 5 to 25 dg/min,wherein the secondary seal stock is configured to remain in a screw capand separate from the primary laminate when the screw cap removed from acontainer.
 47. The primary laminate according to claim 46, wherein abond of the second extruded polymeric adhesive to the secondary sealstock is greater than a bond of the second extruded polymeric adhesiveto the layer of plastic film.
 48. The primary laminate according toclaim 47, wherein a surface energy of a lower surface of the secondaryseal stock is lower than a surface energy of the layer of plastic film.49. The primary laminate according to claim 43, further comprising aplurality of tab stock film layers spaced across the primary laminate.50. A primary laminate configured to form a tabbed sealing member havinga tab defined wholly within a perimeter thereof, the primary laminatecomprising: a seal laminate including at least a bottom layer forsecuring to a rim surrounding a container opening, a foil layer, and atop non-foam polymer layer; a tab stock with a top and bottom facewherein the bottom face of the tab stock is in non-adhesive contact withthe top non-foam polymer layer of the seal laminate to form a primarysubstrate, the tab stock being narrower in width than the seal laminate;an upper surface of the primary substrate having a first and a secondportion wherein the first portion is formed by the top non-foam polymerlayer and the second portion is formed by the top face of the tab stock;a layer of plastic film adhered to both the top face of the tab stockand the top non-foam polymer layer by an extruded polymeric adhesive;and a bond between the layer of plastic film and the top non-foampolymer layer formed by the layer of extruded polymeric adhesive of atleast about 15 N/cm; wherein the tab stock is a laminate of polymerlayers with an adhesive tie layer therebetween.
 51. The primary laminateof claim 50, wherein the layer of plastic film, the top non-foam polymerlayer, and the extruded polymeric adhesive are transparent.
 52. Theprimary laminate of claim 50, wherein the layer of plastic film ispolyethylene terephthalate, polyamide, polypropylene or a compositethereof.
 53. The primary laminate of claim 50, wherein the layer ofplastic film is a coextruded multi-layer film.
 54. The primary laminateof claim 50, wherein the extruded polymeric adhesive is selected formthe group consisting of polyethylene, polyethylene vinyl acetate, maleicanhydride/acrylate ester/polyethylene copolymer, and ethylene methylacrylate.
 55. The primary laminate of claim 50, wherein the top non-foampolymer layer is polyethylene terephthalate.
 56. The primary laminateaccording to claim 50, further including a secondary seal stock havingan overall stiffness in the range from 200-1200 gcm and wherein thelayer of plastic film of the primary laminate is bonded to the secondaryseal stock by a second extruded polymeric adhesive having a melt flowindex of 5 to 25 dg/min, wherein the secondary seal stock is configuredto remain in a screw cap and separate from the primary laminate whenscrew cap removed from a container.
 57. The primary laminate accordingto claim 56, wherein a bond of the second extruded polymeric adhesive tothe secondary seal stock is greater than a bond of the second extrudedpolymeric adhesive to the layer of plastic film.
 58. The primarylaminate according to claim 57, wherein a surface energy of a lowersurface of the secondary seal stock is lower than a surface energy ofthe layer of plastic film.
 59. The primary laminate according to claim56, wherein the secondary seal stock is a laminate having a core layerwith facing layers on opposite sides thereof.
 60. The primary laminateaccording to claim 56, wherein the secondary seal stock is configured toseparate from the primary laminate with an audible cracking indicationupon unscrewing of a cap including a sealing member formed form theprimary laminate to provide audible evidence that the container has notbeen tampered with.
 61. A primary laminate configured to form a tabbedcontainer sealing member having a tab defined wholly within a perimeterthereof, the primary laminate comprising: a seal laminate including atleast a bottom layer for securing to a rim surrounding a containeropening, a foil layer, and a top polyester film layer; a tab stock filmlayer with a top and bottom face wherein the bottom face of the tabstock film layer is above the top polyester film layer of the seallaminate to form a primary substrate; an upper surface of the primarysubstrate having a first and a second portion wherein the first portionis formed by the top polyester film layer and the second portion isformed by the top face of the tab stock film layer; a layer of plasticfilm adhered to both the top face of the tab stock film layer and thetop polyester film layer by an extruded polymeric adhesive, the layer ofplastic film selected from polyethylene terephthalate, polyamide,polypropylene or a composite thereof, and the extruded polymericadhesive selected from polyethylene, polyethylene vinyl acetate, maleicanhydride/acrylate ester/polyethylene copolymer, and ethylene methylacrylate; and a bond between the layer of plastic film and the toppolyester film layer formed by the layer of extruded polymeric adhesiveof at least about 15 N/cm; wherein the upper surface of the primarysubstrate is free of printing that interferes with the bond formedbetween the layer of plastic film and the top polyester film layer;wherein one of the foil layer or an underside of the top polyester filmlayer facing the foil layer is printed so that the printing is not indirect contact with the extruded polymeric adhesive, and the layer ofplastic film, the top polyester film layer, and the extruded polymericadhesive are transparent so that the printing is visible through the topof the primary laminate.